The invention concerns an infinitely variable toroidal drive.
Those infinitely variable toroidal drives usually have, co-axially disposed in relation to a common shaft, input and output discs which are arranged in pairs and have toroidal-shaped inner surfaces, friction wheels situated between the pairs of input and output discs. The friction wheels are in frictional contact both with the input discs and with the output discs and transmit the torque that has been transmitted to them by the input disc to the output disc by frictional contact, the rotational speed of the friction wheels being higher as greater is the distance between their contact point with the input disc and the axis of rotation. On the other hand, the rotational speed of the output disc is higher as nearer the contact point is between friction wheel and output disc to the axis of rotation. Accordingly, the rotational speed of the output disc can be infinitely and arbitrarily set by swiveling the friction wheels. To this end, the axes of rotation of the friction wheels are supported on a carrier which can be controlled via a swiveling device.
The basic principle of such infinitely variable toroidal drives has already been described in U.S. Pat. No. 2,152,796 published in 1939. In this publication two pairs of concave input and output discs are provided between which are disposed swiveling supported friction wheels so that a torque, transmitted via an input shaft to the input discs, and the friction wheels, according to the relative position of the friction wheels with a reduction ratio depending thereon, is fed via the input discs, a gear wheel step and a hollow shaft to a compound gear in the form of a planetary transmission. The web of the planetary transmission drives an output shaft which is connected with the input gears, e.g. of a motor vehicle. At the same time, the output shaft can be disposed parallel to and spaced from the input shaft. The output gear wheel and the two output discs are rotatably supported on a sleeve which, on its ends, is supported in bearing brackets. The arrangement of the bearing brackets between respective input and output shafts presupposes a sufficiently large installation space between the discs.
The transmission according to U.S. Pat. No. 3,739,658 also has a pull-and-push variator with two input and output discs arranged in pairs between which supported friction wheels are tiltingly situated. This construction includes a bearing bracket which is a component part of the housing and is horizontally placed spatially between the two output discs. The power flowing from the output discs is fed to a hollow shaft via a planetary transmission that, in addition, acts as a differential. The hollow shaft is non-rotatably connected with an output gear wheel and is rotatably retained by the ball bearings in the bearing bracket.
The output gear wheel is drivingly connected with a gear wheel which is non-rotatably fastened to the housing of a torque converter. The latter drives the output shaft of the transmission. The arrangement of the torque converter, on the input of the output shaft, causes a relatively large axial distance between input and output shafts of the transmission. Thus, the occasions for use of such transmission are severely limited, since the required installation space is not always available.
U.S. Pat. No. 4,893,517 discloses an Infinitely variable toroidal drive having an input shaft that penetrates a housing. The housing is divided in two hollow spaces, by a partition wall, in each of which an input disc and an output disc opposite each other with friction wheels therebetween are situated, both the input disc and the output disc lie in both hollow spaces on a common axis toward which the friction wheel can be swung to attain the desired speed ratio. The two pairs of input discs and output discs are disposed in mirror symmetry to one another in both hollow spaces so that both output discs are next to each other, specifically at both sides of the partition wall separating the two hollow spaces from each other and in which a gear wheel is supported which is actuated with the output torque jointly by both output discs.
The torque is transmitted, via another gear wheel to a parallel output shaft thereby to penetrate only one of the two hollow spaces and be supported on the partition wall on one end.
The partition wall can be introduced in the housing, together with the appertaining bearings and spacers, and bolted therewith as a pre-assembled unit, however the possibility of preassemblage is limited to a few individual parts. Therefore, the assembly cost for completing the transmission is still considerable. Another disadvantage of this transmission consists in that very strong forces are introduced in the transmission housing, which makes a strong construction with a corresponding heavy weight necessary.
U.S. Pat. No. 5,033,322 also describes an infinitely variable toroidal drive having basically the same design as the above described toroldal, i.e. two transmission units each in the form of an input disc, an output disc and friction wheels pivotably supported therebetween. In order to prevent the carriers of the friction wheels of the other transmission unit from being exposed to vibrations, in such a toroidal drive whenever one transmission unit is controlled by the control device, a mechanical device is provided in this known toroidal drive. The mechanical device prevents reciprocal movement of the first pair of carriers for the friction wheels and the second pair of carriers for the friction wheels. The device consists of upper and lower transverse links (i.e. yokes) which accommodate the bearings for the carriers (pivots) of the friction wheels and which are swingingly disposed around pivots fastened to the housing. In order to eliminate movement relative to one another, the transverse links are rigidly interconnected by rods extending in a longitudinal direction. Vibrations, acting upon the carriers due to the friction wheels, are limited so that the slip on the second transmission unit is reduced.
The problem to be solved by this invention is to provide a toroidal drive in which assemblage is considerably easier so that the production costs are reduced and which has slight weight.
The inventive transmission offers the advantage that the largest part of the forces introduced are absorbed by the frame so that the housing is unburdened. The pre-assemblage of the essential parts on the frame makes easier and accelerates the construction of the toroidal drive, since the frame with the pre-assembled parts, after being introduced in the housing which can be designed considerably lighter than the traditional housing, has to be connected with the latter only on a few places.